Spatial distribution of heavy metals in the abandoned tailings pond of Chaihe lead-zinc mine

摘要

Chaihe lead-zinc mine lies in Laoning province,Northeast China,and its tailings pond has been abandoned 22 years ago,growing a small amount of weeds.On the tailings site,5 sampling points of P1,P2,P3,P4 and P5 were set at intervals of 100 m along the discharge direction of tailings slurry from upstream to downstream,and the samples were taken at every layer to 20 cm interval in the depths of 220 cm for each sampled point.For every sample,pH,total content of heavy metal and acid soluble fraction were determined following the standard methods.Results showed that the pH values of the tailings ranged from 6.83 to 7.97,which increased with depth in 0-120 cm; below 120 cm,there was a vibration,and on the whole,there were a little higher in the downstream samples.Pb,Zn and Cd are the major contaminants in the tailings and the mean content of Pb was 1372.79 mg/kg,Zn was 4077.15 mg/kg and Cd was 49.74 mg/kg.Total contents of Pb,Zn and Cd at P4,P5 in the downstream were higher than the contents at P1,P2 and P3 in the upstream.In 0-60 cm,total contents and acid soluble fraction contents decreased with depth at P1,P2,P3 and P4,and there were insignificant variations in tailings below100 cm.Furthermore,the contents of Pb,Zn,and Cd significantly increased in most layers of P5,which could be due to the railings discharge.The proportions of Pb and Zn for acid soluble fraction to total content were higher at downstream sampled points than upstream ones.The results can serve for the measure of railings pond reclamation.